How does polarization of light improve a sunglasses
quality? Or the "sunglass experience", so to speak -
That is, I presume the usual definition - the lens
passes light polarized along a single direction.
--
Rich
How does polarization of light improve a sunglasses
quality? Or the "sunglass experience", so to speak -
That is, I presume the usual definition - the lens
passes light polarized along a single direction.
When light reflects obliquely off a dielectric surface, such as water or
the shiny hood of your car, the reflection is partially polarized,
usually with the vertical polarization much weaker than horizontal.
That means that the electric (E) field is vibrating mostly in the
horizontal direction. (I'm assuming that the surface is horizontal and
the light is coming from above, which is the usual situation outdoors.)
So the glints are polarized and the rest of the scene mostly isn't. (*)
Thus polarizing filters that absorb the horizontal polarization
selectively reduce the glints.
The reason is interesting. The electric field of a light ray
oscillates, but is directed perpendicular to the propagation direction.
At an interface between two non-absorbing dielectrics, the reflected and refracted beams go in different directions, but their fields have to add
up to the same as the incident wave. The addition is vectorial, so
there's a difference between horizontal polarization, which stays horizontal, and
vertical, which has to change directions on account of the change in propagation direction.
It turns out that when the reflected and refracted rays are at 90
degrees to each other, in vertical polarization the reflection goes to
zero and in horizontal polarization it doesn't. The incidence angle
where this happens is called "Brewster's angle" after its discoverer.
On April 7, Phil Hobbs wrote:
How does polarization of light improve a sunglasses
quality? Or the "sunglass experience", so to speak -
That is, I presume the usual definition - the lens
passes light polarized along a single direction.
When light reflects obliquely off a dielectric surface, such as water or
the shiny hood of your car, the reflection is partially polarized,
usually with the vertical polarization much weaker than horizontal.
That means that the electric (E) field is vibrating mostly in the
horizontal direction. (I'm assuming that the surface is horizontal and
the light is coming from above, which is the usual situation outdoors.)
So the glints are polarized and the rest of the scene mostly isn't. (*)
Thus polarizing filters that absorb the horizontal polarization
selectively reduce the glints.
So this type of filter removes the bit we commonly call glare.
But there's no free lunch. So what's the loss or cost?
The reason is interesting. The electric field of a light ray
oscillates, but is directed perpendicular to the propagation direction.
At an interface between two non-absorbing dielectrics, the reflected and
refracted beams go in different directions, but their fields have to add
up to the same as the incident wave. The addition is vectorial, so
there's a difference between horizontal polarization, which stays horizontal, and
vertical, which has to change directions on account of the change in
propagation direction.
It turns out that when the reflected and refracted rays are at 90
degrees to each other, in vertical polarization the reflection goes to
zero and in horizontal polarization it doesn't. The incidence angle
where this happens is called "Brewster's angle" after its discoverer.
I'm familiar with Brewster angle, but unclear how it affects
sunglass performance, i.e. the subjective experience.
--
Rich
On April 7, Phil Hobbs wrote:
How does polarization of light improve a sunglasses
quality?
I'm familiar with Brewster angle, but unclear how it affects
sunglass performance, i.e. the subjective experience.
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